http://www.ft86club.com/forums/showthread.php?t=11682
This has been happening since 2012 including myself. I got it replaced under warranty. If you leave it alone, it will get worse. I don't know how much of a help it will be to put some kind of grease since the rubber piece is already deformed. For mine, I had to get out of the driver seat, go around to the passenger seat, close the door while holding the weather strip, then finally get out of the passenger seat. Otherwise, the window wouldn't close properly.
My warranty is out too now and if this happens again (or the passenger side), I would like to do it myself. So, I'm interested in DIY too.